Various methods are known and recognised as being effective for controlling the growth of weeds and other undesirable substances. These methods are used in the agricultural industry and also by state and government bodies such as local councils for keeping paths and other areas free from weeds. Many existing methods involve the application of aqueous solution of chemicals onto the weeds. Recently, the application of chemical weed killers has become less desirable, both from a health and safety point of view in terms of the health of the person applying the chemicals, but also from the point of view of the damage to the environment caused by the use of chemicals.
One known method for killing weeds which does not utilise chemicals, is the application of steam and/or hot water to kill vegetation. U.S. Pat. No. 213,255 (Simpson) for example, discloses an apparatus which uses steam and/or hot water to kill vegetation on railroad beds.
Australian patent application No. 65573/99, entitled “A method of generating a treatment fluid” discloses a method for combining compressed air with heated water at an applicator nozzle.
A number of other patents also describe apparatus for applying heated pressurised water to vegetation including AU 668291 which discloses an apparatus for controlling vegetation by the application of a high pressure water or liquid spray delivering the liquid to a spray tip at a pressure of 100 psi to about 4,000 psi. AU 709493 discloses a method of killing or controlling weeds in which pressurised hot water is applied to weeds of a temperature of 75° C. or above delivered at a pump pressure of in excess of 200 psi and at a flow rate in excess of 4 liters per minute.
However, one major problem with existing hot water and steam applicator and generator means, is that a considerable amount of energy is required to heat the water due to the high specific heat capacity of water and the even higher specific latent heat as water changes from a liquid to a gas, thus the energy consumption of such devices is a major disadvantage of hot water or steam weed control.
An apparatus that was able to control or kill weeds using a smaller volume of water, would not only be more efficient in terms of use of water as a commodity but also more energy efficient.
Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.